In many instances it is desirable that the medicament delivery device is capable of delivering a certain specified quantity of the medicament. This is for example the case with a multi-dose injection device, which is capable of delivering a number of specified, set, doses until the compartment is empty. One example is disclosed in the European patent application publication No. EP 1 218 042, where specific doses can be set before injection by turning a dose setting button on the distal end of the injector.
If however a dose is set too high, i.e. the user overshoots the desired dose, the device has to be reset so that a user may set the proper dose. According to EP 1 218 042 this is done by continuing the rotation of the dose setting knob until it is moved past the maximum value, past which the dose setting knob is released. It is then possible to rotate back the dose setting knob to the initial, or zero, position, at which position the dose setting knob is re-connected to the dose setting mechanism.
A clear drawback with the solution according to EP 1 218 042 is that if the dose is overshot, the dose knob has to be rotated the whole way to the end position and then rotated back to the zero position, and then again turned to the desired dose. Thus, if a dose setting is missed a lot of rotation is required in order reset the device and set the dose. Further the design requires a number of inter-acting components in order to achieve the desired function.
WO 2006/045526 relates to a device employing a so called dial-down mechanism to reduce a set dose in incremental steps. During dial-up, i.e. increasing the dose, WO 2006/045526 relies on an arm to slide over teeth arranged on the inside of a nut in order to flex against the teeth in a locking state upon arrival at the preferred dose.
The drawback of this solution is that as the arm slides against the teeth it will eventually wear down and the force bias against the teeth, which is based on the inherent material properties and the design of the arm, will be reduced over time, resulting in reduced reliability of the locking mechanism of the arm against the teeth. Also, since WO 2006/045526 uses a curved profile for the teeth and for the connecting member of the flexible arm this reliability problem is worsened.
There are thus a number of aspects that are addressed with the present invention.